精确分析任意导体地面上的套筒单极子天线

利用矩量法分析任意形状导体地面上的套筒单极子天线.对面结构选用三角形面元矢量基函数,对细线结构选用三角基函数,对线面结合处采用一种特殊的基函数,将导体地面和天线作为整体进行分析,大大提高了分析计算的精度.分别分析了两付位于圆形和方形地面上的实用套筒天线,其数值计算结果与实验结果或软件模拟结果吻合良好,表明了该方法的有效性.     

组合导体平台前线天线的混合MoM-PO分析

运用混合矩量法-物理光学法分析了组合导体平台附近线天线的电磁辐射特性,对线天线采用窄带结构建模,计算时整个区域都选用RWG基函数,避免选用其他形式的基函数,从而简化计算,并推导出计算公式。利用该方法计算了几种导体平台前线天线的辐射特性,通过和MoM、FEKO计算结果的对比,数值结果验证了混合方法的可行性与有效性。     

一种加载圆锥单极子天线的设计与实现

介绍了一种加载圆锥单极子天线的设计,加载圆锥单极子天线具有形式简单、频带宽、交叉极化低和增益高的优点.通过电磁仿真软件,计算了天线的驻波比和方向图随频率的变化规律.分析表明文中的天线超宽带、全向,满足驻波比的要求,具有良好的应用前景.     

模式匹配法分析有限圆盘地面单极天线

本文给出了一种严格分析有限尺寸圆盘地面单极天线的新方法———模式匹配法 .该方法通过在天线上、下两边平行放置两个无限大良导电平面 ,以及合理划分区域 ,使得每个分区中的场分量能够采用柱谐展开式解析表示 ,且展开系数由导体表面边界条件及分区交界处场分量连续条件加以确定 .在此基础上 ,进一步分析天线的输入阻抗等电性能 .计算结果表明 :对不同尺寸圆盘地面单极子天线 ,理论分析与文献中的实验结果均十分吻合 .同时 ,由于场量的解析表示 ,使得计算速度较快     

车载宽叶单极对数周期天线的矩量法分析

将单极对数周期天线改进成宽叶形式,使之具备更好的电气性能和机械性能,从而适合于车载使用.利用矩量法分析了这种车载宽叶单极对数周期天线,其面结构选用RWG矢量基函数,细线结构选用三角基函数,将导电载体和天线作为一个系统进行分析,运用传输线网络理论解决了天线振子馈电问题.最后进行实例计算,计算结果与实际测量结果吻合良好,验证了该方法的有效性.     

基于遗传算法的套筒单极子天线的优化设计

研究了套筒单极子天线的优化设计。文中采用将圆盘地面和套筒单极子天线整体分析的计算模型 ,运用矩量法结合基于小生境技术的遗传算法对其进行优化设计。最后 ,设计出一种工作在 110 - 390MHz频段、VSWR <3.0的实用套筒天线 ,分析计算结果与实验结果吻合良好 ,验证了本文方法的有效性和实用性。     

模式匹配分析有限圆盘地面单极天线

本文给出了一种严格分析有限尺寸圆盘地面单极天线的新方法－模式匹配法。该方法通过在天线上、下两边平行放置两个无限大良导电平面,以及合理划分区域,使得每个分区中的场分量能够采用柱谐展开式解析表示,且展开系数由导体表面边界条件及分区交界处场分量连续条件加以确定。在此基础上,进一步分析天线的输入阻抗等电性能。计算结果表明：对不同尺寸圆盘地面单极子天线,理论分析与文献中的实验结果均十分吻合。同时,由于场量的解析表示,使得计算速度较快。     

线面结构天线的电磁建模与计算

应用矩量法对线面结构的天线进行建模,针对天线中的不同结构,选用了不同的基函数进行建模,对于线结构和面结构,分别采用了经典的三角形基函数和RWG 矢量基函数。而对于线面结合处这一复杂结构,在分析传统线面基函数表达式的基础上推导出一种新的基函数,该基函数中增加了描述天线粗细的项,且其散度为一常数,避免了复杂的差分计算,有效解决了传统线面结合基函数分析粗天线模型时误差大且存在奇异点的缺点。在此基础上,给出了线面结构天线阻抗矩阵及散射场的计算方法。最后通过两个天线的算例验证了该算法的正确性和通用性。     

HFSS/UTD混合法计算电大尺寸导体上的天线

采用高频方法一致性绕射理论(UTD)与电磁场计算软件HFSS相结合的方法,提高HFSS在计算电大尺寸导体上的天线时的效率和精度。文中以圆形地面上的单极子天线为例,说明了该方法的实用性。     

任意形状线、面、体组成导体目标的电磁建模

本文用积分方程和矩量法分析具有任意线、面、体组成的理想导体目标的电磁散射和辐射特性.其中统一采用RWG基函数对线、面、体导体上的电流进行展开;对于任意的线-面,面-面连接情况,根据电流连续性条件,给出了通用的设置基函数和未知量的方法;对于辐射问题,给出了设置激励源与计算输入阻抗的方法.最后通过分析导体盒上的单极天线和宽带贴片天线验证了本文方法的可行性和有效性.     

计算曲线天线电流分布的一种新途径─参数形式下的B样条有限元法──Ⅱ：应用实例─多臂螺旋天线的电流分布

多臂螺旋天线由于其宽频和多模特征，它在空中和地面天线系统中得到了广泛的应用。本文详细描述了基于第一部分提出的参数形式下的Ｂ样条有限元法计算等角螺旋天线和阿基米德平面螺旋天线电流分布的实施过程。通过与有关文献比较，计算实践表明本文方法具有实施简便、计算量少等优点。     

The radiation efficiency of a dipole antenna located above an imperfectly conducting ground

The dyadic Green's function technique is used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane. The three antennas treated are: 1) vertical Hertzian dipole, 2) horizontal Hertzian dipole, and 3) a vertical half-wave dipole with sinusoidal current distribution. The results of numerical evaluation of the integral expressions for several values of ground constants are presented in graphical form. The radiation efficiency of a vertical Hertzian dipole is found to exhibit a distinct peak when located at a height of one-eighth wavelength.     

Conical Double-Dielectric Fresnel Zone Lens and Antenna

A conical double-dielectric phase-reversal Fresnel-zone plate (FZP) lens is introduced. We present the lens design equations as functions of cone opening angle. As an example, the phase-reversal lens has been applied to four millimeter-wave antennas with different lens opening semi-angles: 45deg, 60deg, and 75deg (conical lenses) and 90deg (plane lens). The radiation characteristics of these antennas have been calculated and contrasted one-to-another, and to those with the same semi-angles and linear dimensions binary (half-open) FZP lens antennas. The double-dielectric FZP conical arrangement can serve as a conical antenna lens and a radome simultaneously     

Accurate Evaluation of Magnetic- and Electric-Field Losses in Ground Systems

The efficiency of ground-based antennas is highly determined by the power dissipated in the ground plane, which can be separated into H-field and E-field losses. In this paper, a new approach is presented for the separation of ground losses that is based on Joule's law. It is theoretically valid at any frequency. Nevertheless, some simplifications can be applied in the low-and medium-frequency bands, where the Earth's soil behaves like a good conductor. In the analysis, the antenna's ground plane has been divided into two zones: a) the artificial ground plane, where a radial-wire ground screen was used; and b) the natural ground plane or bare soil, up to a circular boundary a half wavelength from the antenna's base. In order to avoid overestimating the penetration of fields in the artificial ground plane, the previous theory has been extended by introducing the concept of effective skin depth. The monopole's nonzero equivalent radius effect has been taken into account by means of a modified current distribution. Also, the case of short top-loaded antennas has been treated. H-field and E-field losses have been analyzed by means of equivalent resistances and computed numerically as functions of frequency in the LF and MF bands for different antenna dimensions, ground screens, and soil physical conditions. Some results have also been obtained by Moment-Method simulations.     

Accurate computation of the radiation from simple antennas usingthe finite-difference time-domain method

Two antennas are considered, a cylindrical monopole and a conical monopole. Both are driven through an image plane from a coaxial transmission line. Each of these antennas corresponds to a well-posed theoretical electromagnetic boundary value problem and a realizable experimental model. These antennas are analyzed by a straightforward application of the finite-difference-time-domain (FD-TD) method. The computed results for these antennas are shown to be in excellent agreement with accurate experimental measurements for both the time domain and the frequency domain. The graphical displays presented for the transient near-zone and far-zone radiation from these antennas provide physical insight into the radiation process     

Simplified calculation of ground losses in low- and medium-frequency antenna systems

Calculations of ground losses are paramount in obtaining the best performance of a monopole antenna in the low- (LF) and medium-frequency (MF) bands. Ground losses are usually computed numerically, due to difficulties in the mathematical formalism. The novel approach here permits obtaining simple analytical expressions for ground-loss calculations that can be useful for determining the behavior of the ground plane. As a first approximation, the monopole antenna is placed on a perfect electrically conducting (PEC) ground plane in order to obtain the antenna current distribution and the near magnetic field, taking into account the non-zero-radius effect of the monopole. Next, the near magnetic field is used to determine the surface-current density on the ground plane below the antenna. This is divided into two zones: (1) the artificial ground plane, where either a radial-wire ground screen or a metallic layer is used to increase the soil's conductivity; and (2) the natural ground plane or bare soil up to a circular boundary a half wavelength from the antenna's base. The power dissipation is calculated from the artificial and natural ground-plane surface-current densities, and the ground-plane loss resistance is obtained. Also, an effective conductivity is defined as a measure of the ground plane's effectiveness, and the cases of quarter-wave monopoles and short top-loaded antennas are analyzed. Some results are validated by means of numerical computations and moment method simulations     

Dielectric image line groove antennas for millimeter waves, Part II: Experimental verification

In the first part of this paper the theory of radiation from discontinuities in the ground plane of a dielectric image line has been described. In this second part experimental verifications of the radiation theory as well as millimeter-wave antennas realized on the basis of the theory are described. In the antennas slots and holes in the ground plane of the dielectric image line are used as discontinuities. Experimental results for the radiation characteristics are discussed.     

A Miniaturized Ground Edge Current Choke—Design, Measurement, and Applications

We propose a miniaturized microwave current choke for blocking the current flowing along the edge of a substrate's ground plane. The proposed current choke is composed of a printed inductor and a printed capacitor, which possesses a size much smaller than a conventional quarter-wavelength current choke. By introducing the choke at one side of the ground plane, an effective electrical open circuit is performed for reflecting the ground edge current. The size of the proposed ground edge current choke (GECC) is as small as around 0.06 wavelength in free space. Two applications of the GECC are presented in this paper. The first is the radiation pattern regulation of a printed monopole antenna with long ground plane. The GECC in this application reflects the induced traveling-wave current along the ground plane edge and changes it to a standing-wave one, thus regulating the tilted radiation pattern due to the traveling-wave current to a broadside pattern. The other application is the decoupling of two nearby monopole antennas. By placing the proposed compact GECC in between the antennas, it is found that the isolation between the antenna ports can be enhanced from 8 dB to 32 dB. The experimental results agree well with the simulation, which demonstrate the feasibility of the proposed GECC.      

Numerical modeling of ultrawide-band dielectric horn antennas using FDTD

A detailed characterization of the input impedance of ultrawide-band (UWB) dielectric horn antennas is presented using the finite-difference time-domain (FDTD) technique. The FDTD model is first validated by computing the characteristic impedance of two conical plate transmission lines (including planar bow-tie antennas) and comparing the results to analytical solutions. The FDTD model is next used to calculate the surge impedance of dielectric horn antennas using the conical plates as launchers. Design curves of the surge impedance for different choices of geometries and dielectric loadings are provided. The modeled antennas are particularly attractive for applications such as UWB ground penetrating radars (GPR) applications.